The Dynamics of San Diego’s Water Supply

With water being an increasingly precious commodity in San Diego, as well as all over the world, understanding the dynamics of water supply is critical.

For starters, San Diego has three primary sources of water (2011 statistics):

30 percent is imported from the Sacramento San Joaquin Bay Delta

54 percent is imported from the Colorado River

16 percent is from local sources

Some factoids of interest include:

An acre foot of water contains 326,000 gallons of water and can serve a typical family of four for one year.

Water customers are charged by units of one hundred cubic feet of water (HCF) or 748 gallons.

While local rainfall helps defray the cost of water, it not a major source of San Diego’s supply, contributing less than ten percent.

A January 2012 survey revealed that 78 percent of Californians and 86 percent of Southern Californians have never heard of or know anything about the Bay Delta despite its importance to state water supplies.

San Diego receives Colorado River water through the Metropolitan Water District of Southern California which has an annual allocation of 550,000 acre feet. The San Diego County Water Authority has arranged for transfers of additional Colorado River water from several Imperial County water agencies. While Colorado River flows are critically important, these supplies to San Diego come from allocations that would be among the last to be cut.

San Diego used 525,000 acre feet of water in 2011, 122,000 acre feet less than the 647,000 acre feet used in 1990. This despite the additions of approximately 500,000 residents, a nearly 20 percent growth in population. The reduced use of water has been primarily achieved by a decline in agricultural use from 19 percent to 8.4 percent and through urban conservation.

The cost of water has become a compelling question for many San Diego area customers. It is counter-intuitive that even while they are saving water, their bills are going up. Three factors explain this:

Not long ago, imported water cost between $400 and $500 an acre foot. Now new water supplies can be double or triple that cost. Desalinated water will exceed $2,000 an acre foot, and reclaimed water is also more expensive.

Even if customers use less water, the infrastructure to deliver that water must be operated and maintained. This includes reservoirs, pump stations, pipelines and the cost of energy to move water. As less water is used, the unit cost of the water increases and the resulting burden must be shared by everyone.

To encourage conservation, tiered water rates have been established in most water districts. These rates are low for the first increment of water used, but become significantly more expensive as customers move into higher tiers, even if they are using less water overall.

San Diegan’s have long felt that they are particularly vulnerable because the region is dependent on imported water. While that dependency is being buffered by the development of local sources of supply, San Diegans are not alone in their concerns about water security.

Questions about the future cost and availability of water are being asked around the world. Groundwater supplies are being utilized unsustainably from the U.S. Midwest to the Indian subcontinent. This decrease in supply coupled with an increase in global demand and the inter-relationship between the cost of energy and the cost of water mean that water supply issues will be on the policy agenda far into the future.

This article was first published in the January/February 2013 issue of Air2Air Magazine.